Susan L. Mullis, charged with murdering her husband on a lonely dirt road in a remote part of Fairfax County, took the stand yesterday and said that although she had talked about wanting her husband killed, she had done so "in a joking way."

With some members of the Fairfax County Circuit Court jury leaning forward to hear, assistant prosecutor Raymond F. Brownelle asked: "Did you ever talk about having your husband killed?"

"I don't know how to phrase this," the defendant responded. "Several times when I was upset with my husband I said that. I didn't mean anything by it . . . . It was in a joking way. It was never an elaborate thing, like 'let's sit down and make plans.' "

On Monday, a former boyfriend testified that Mullis had tried several times to get him to arrange her husband's death.

Under questioning from her own attorney, Steven A. Merril, she said she did not kill her husband and had no idea who killed him or why.

Michael R. Mullis, a 29-year-old pharmacist who lived with his wife in Woodbridge, had driven with her to a remote part of Fairfax County on the night of July 23, 1983.

Susan Mullis, 28, testified that she had left the car to relieve herself in the woods when she heard shots, returned to the car, found her husband shot and ran to get help.

Police have not found the weapon.

The Mullises were scheduled to legally separate the week after Michael Mullis was killed, according to testimony. At the time of his death, they had been estranged for more than a year, living in different parts of their house.

Susan Mullis testified that, at her husband's direction, she drove to the remote area where he was killed, and that just before she left the car, both she and her husband "heard voices."

Her attorney told the jury that Michael Mullis was a drug abuser with severe mental problems. "Why he went to that location, Sue doesn't know," Merril said. "Did he meet somebody for a drug deal? Did he see something he shouldn't see? Was it a random killing? Sue doesn't know. Unfortunately, the police don't know either."

The case is expected to go the jury today.